Catalytic desulfurization of petroleum hydrocarbons



Patented June 2, 1953 CATALYTIC DESULFURIZATION OF PETROLEUM HYDROCARBONS Frederick William Bertram Porter and Roy Purdy Northcott, Sunbury-on-Thames, England, assignors to Anglo-Iranian Oil Company Limited, London, England, a British joint-stock corporation N Drawing. Application November 7, 1950, Se-

rial No. 194,578. In Great Britain November 2 Claims. (Cl. 196-28) This invention relates to the catalytic desulphurization of cracked petroleum naphthas obtained from thermal or catalytic cracking processes.

It is known to desulphurize hydrocarbons by passing them in admixture with hydrogen over a sulphur-resistant desulphurization catalyst at elevated temperature and pressure whereby organic sulphur compounds present in the hydro.- carbons are hydrogenated to form hydrogen sulphide which can be readily removed, from the treated hydrocarbons. The process may be called hydrofining and as normally carried out involves a net consumption of hydrogen and the cost of supplying the hydrogen is a major factor in the economics of the process. Furthermore in order to secure the necessary partial pressure of hydrogen, it has generally been considered necessary to operate at elevated pressure ranging from.500- 1000 lb./sq. in. or more, and a plant'to withstand such pressures has to be made from special steels which are comparatively expensive.

It is well-known that the reforming or hydroforming process as applied to straight-run naphthas effects considerable desulphurization and at the same time produces hydrogen mainly by dehydrogenation of the naphthenes present. This process is carried out at elevated temperatures of, for example, between 800 and 1100 F. in order to securean appreciable formation of aromatics and does not constitute an economic desulphurifzation process in view of the fact that the reac tion conditions are so severe that the catalyst has a very short active life and needs to be regenerated at short intervals of about 6 hours, while the increased production of aromatics is in many cases undesirable. It has also been proposed to treat a catalytically cracked naphtha in admixture with a straight-run naphtha, the latter being dehydrogenated under the conditions of the reaction to provide hydrogen for the hydrogenation of unsaturated components of the cracked naphtha. Ifthe cracked naphtha contains sulphur, the sulphur is removed. to some extent but the process is not primarily a desulphurization process, and has the disadvantages of requiring an extraneous source of naphthene.

From work carried out on the hydrocatalytic .desulphurization process, it was known that the amount of hydrogen required for desulphurization was small, being of the order of '70 cu. ft./bbl. for the removal of 1.0 per cent weight sulphur in the feedstock. All crude oils contain naphthene hydrocarbons in varying degree throughout the boiling range and it was considered that if the dehydrogenation of those naphthenes could be carried out under mild conditions to ensure long onstream hours, then hydrofining should be possible at the same time and the desulphurization reaction could become self -supporting with respect to hydrogen. From the meagre thermodynamic data available it was known that dehydrogenation of six membered ring naphthenes was theoretically complete above 350 C. and that the recycle of hydrogen, per :36, had little eiiect on the reaction but increase in hydrogen partial pressure retarded the reaction, having a marked effect above 250 p. s. i.

The invention therefore has among its objects to provide a process for the desulphurization of cracked naphthas which can be carried out without the use of hydrogen or hydrogen donor added from an external source. It is also an object of the invention to enable such a process to be carried out at pressures low enough to avoid the use of special pressure-resisting steels, thereby reducing the cost of the plant.

Yet another object of the invention is to .ensure that the conditions of operation are such that little or no molecular breakdown occurs and that the product, except for sulphur elimination, has properties and boiling range similar to the feedstock. 7

According to the invention, there is provided a process for the catalytic desulphurization of a cracked naphtha, wherein the cracked naphtha is passed in vapour form in admixture with hy- ,sulphide and,to supply the hydrogen require- 3 ments in the reaction zone, a hydrogen-rich gas mixture being separated from the treated cracked naphtha and recycled to the reaction zone to constitute the whole of the hydrogen supplied to said zone.

As indicated above, the reaction proceeds by dehydrogenation of some of the naphthenes present in the feedstock to produce hydrogen in excess of that required to convert the combined sulphur present into hydrogen sulphide and the reaction conditions for any particular feedstock must therefore be determined having regard to any limiting conditions imposed by these two reactions. Thus, there is a lower temperature, of about 650 F., below which little dehydrogenation would occur and below which the reaction would not be self-supporting in hydrogen. This lower temperature depends to some extent on the sulphur content, and the hil her the sulphur content the higher the minimum temperature necessary to provide sufiicient hydrogen. At temperatures above about 300 F., dehydrogenation ocours to such an extent that the product becomes increasingly aromatic. Furthermore at temperatures above 800 F. the oil-stream time before regeneration is reduced. The preferred temperature of operation is to some extent dependent on the pressure employed which should be between and 500 lb./sq. in. As the pressure is increased, the minimum temperature at which satisfactory dehydrogenation of the naphthenes can be obtained increases.

The space velocity should be maintained in the region of 0.5 to 1.0 v./v./hr.

Desulphurization of cracked napthas by means of hydrogen derived from the feedstock is best achieved under the following set of conditions:

Pressure 2545 p.s.i.ga. Temperature 780-800 F.

Space velocity 0.5 to 1.0 v./V./hr. Recycle rate 109 -4000 C. F./B.

Operating under the conditions above described, the gases separated by cooling the treated naphtha at reaction pressure contain a high proportion of hydrogen and are continuously recycled to the reaction zone. It has been found that the hydrogen sulphide contained in the separated gas builds up to an equilibrium concentration after which the gases may be recycled to the reaction zone without further increase in the content of hydrogen sulphide which is thereafter dissolved in the product until such time as it is depressurised. If desired, however, the hydrogen sulphide may be removed from the gas by any of the usual methods and. the Has-free gas recycled to the reaction zone. The gases may be submitted to treatment for increasing the relative proportion of hydrogen therein, as by passage through an oil tower. It is not necessary to supply extraneous hydrogen to the reaction zone when starting the process as the gases separated from the treated naphtha may be allowed to build up to form the recycle gas.

The preferred catalyst consists of a mixture of the oxides of cobalt and molybdenum, or a chemical compound of cobalt, molybdenum and oxygen, or a mixture of one or both of said oxides with said compound, as such, or incorporated with a support. A particularly effective catalyst consists of a chemical compound oi cobalt, molybdenum and oxygen, or a mixture of said compound with molybdenum oxide, supported on alumina.

A pelleted catalyst was prepared by mixing powdered cobalt oxide, molybdic oxide and aluminaand pelleting with 1% graphite into r t" pellets. The pellets were heated for two hours at 530 C.

Other sulphur-resistant catalysts which are active for the dehydrogenation of naphthenes and the hydrogenation of organic sulphur compounds under the reaction conditions may also be employed. Examples of such other catalysts are molybdenum oxide on alumina, tungsten nickel sulphide (a mixture of tungsten and nickel sulphides) and molybdenum sulphide.

Under the conditions of the process, cobalt and molybdenum oxides and cobalt molybdate react with hydrogen sulphide so that the oxygen is partly displaced by sulphur. This replacement in no way detracts from the activity of the catalyst and possibly even enhances it.

The invention will now be described with reference to the following examples.

Example I A cracked naphtha having a final boiling point of 220 C. A. S. T. M. obtained by catalytically cracking an Iranian wax distillate constituting 5532-861 3 0 by volume of the crude at 55% 430 Dd-L conversion level was passed at a space velocity of 0.5 v./v./hr. to a reaction zone containing a supported cobalt molybdate catalyst and maintained at a temperature of 780-800 F. The

process was operated under equilibrium process conditions, that is to say, the hydrogen separated from the treated naphtha was recycled to the reaction and the pressure therein allowed to build up to an equilibrium pressure. Under the conditions, above described, it was possible to operate the reaction zone at a pressure of 30 p. s. i. ga. and with a recycle rate of 1500 C. F./B. The feedstock had a sulphur content of 0.221% by weight and this was reduced to 0.1 5% by weight over a period of 50 hours on stream. The yield of treated product was over 99% by weight.

Examination of the product after redistillation to 200 C. A. S. T. M. end-point and inhibiting with /1000 bbl. Dupont 22,- yielded the fol- Sulphur, percent wt.

Example [I A pressure distillate of 52-220 C. A. S. 'I. M. boiling range, prepared by visbreaking a 52% Iranian residue at conversion to 4.4% by weight of and gasoline boiling below C., was passed at a space velocity or 110 V./v./hr. to a reaction zone containing a supported cobalt molybdate catalyst and maintained at a temperature of 800 F. and a pressure of 60 p. s. 1. ga, the gas recycle rate being 2000 C.- F./B. The sulphur contained in the feedstock was 0.506% by weight and the average sulphur content in the treated product was 0.17% by weight over 20' hours on stream, giving a sulphur removal or ee%.

Examination of theroduct after reruniiiiig to 200 C. A. T. M. end point and inhibiting with S 0.01% by volume of tricresol, yielded the following inspection data:

Feedstock Product Yield, percent wt. on Feedstock 100.0 88. 2 Specific Gravity, 60 F./60 F 0.7555 0.7465 I. B. P., C 52.5 54.5 10% vol. 0.. 80.5 80 50% vol. C 149 138. 5 90% vol. C 207 191 B. P., C 220. 5 206 Gum Existent, mg./l ml 20 Gum (E-l-P) 120, Lug/100 ml 130 12 S. I. L. Breakdown Time, min 65 180 A. S. T. M. Induction Period, 85 180 Octane No. (MM) 60 62.3 Sulphur, percent wt 0. 506 0. 160

Example III A cracked naphtha having a boiling range of 130-230 C. A. S. T. M. obtained by catalytically cracking an Iranian wax distill-ate to 53.7% volume 430 conversion, was passed at a space velocity or 1.0 v./v./hr. to a reaction zone containing a supported cobalt molybdate catalyst and maintained at a temperature of '780" F. The hydrogen separated from the treated naphtha was recycled to the reaction zone and allowed to build up to an equilibrium pressure. Under the conditions above described, it was possible to operate the desulphurization zone at a pressure of 25 lb./sq. in. and a recycle rate of about 3000 C. F./B. The feedstock had a sulphur content of 0.489% wt. and this was reduced to 0.326% wt. after 18 hours on stream. The yield of desulphurized product was 98.6% wt. on feedstock.

Examination of the product after rerunning to 215 C. A. S. T. M. and inhibiting with 0.04% volume tricresol yielded the following inspection data:

Feedstock Product Yield, percent Wt. on Feedstock" 100.0 88. 2 Specific Gravity, 60 F/60 F.-. 0.8450 0.8280 1. B. P., C 125. 5 111 vol. C 140 128 50% vol. C 1 170 154.5 90% V01. C"--. 218 192. 5 F. B. P., C 230.5 211 Gum Existent, rug/100 ml 59 3 Gum (E+P) 120, mg./l00 ml 154 40 A. S. '1. M. Induction Period, min 150 190 Sulphur, percent wt 0. 489 0.113

We claim:

1. A process for the hydrocatalytic desulphurization of a sulphur-and-naphthene containing cracked petroleum naphtha, which process is self supporting with respect to the hydrogen needed and is productive of a desulphurized cracked naphtha having, except for lowered sulphur content, properties and boiling range substantially the same as the feedstock, comprising the steps of: passing the sulphur-and-naphthene containing cracked naphtha at a space velocity of from about 0.5 to about 1.0 v./v.,-hr. to a reaction zone and contacting the cracked naphtha therein With a dehydrogenation-hydrogenation catalyst and with hydrogen derived solely from the cracked naphtha, said catalyst being resistant to sulphur poisoning and combining activity for the dehydrogenation of naphthenes in said cracked naphtha with activity for the hydrogenation of organically combined sulphur in said cracked naphtha to hydrogen sulphide; establishing a temperature in said zone in the range of from between about 780 F. to about 300 F. at which hydrogen is produced continuously from said cracked naphtha; establishing a pressure in said zone in the range of from about 25 to about lbs/sq. in. gauge, the temperature and pressure established Within said ranges being correlated to provide, from the dehydrogenation of naphthenes contained in said cracked naphtha, hydrogen in an amount at least equal to but not substantially in excess or that required to effect conversion of said organic sulphur compounds to hydrogen sulphide and to supply the hydrogen requirements in said reaction zone; separating a hydrogen-rich gas mixture from the treated product, recycling said hydrogen-rich gas miXtLHe to said reaction zone at a rate in the range of from about 1000 to about 4000 cu. ft./bbl. at which the necessary partial pressure of hydrogen will be maintained in said zone, said mixture constituting the Whole of the hydrogen supplied to said zone; and, recovering the desired cracked naphtha product from the residue of said separating operation.

2. A process in accordance with claim 1 in which the catalyst comprises cobalt molybdate supported on alumina.

FREDERICK WILLIAM BERTRAM PORTER. 

1. A PROCESS FOR THE HYDROCATALYTIC DESULPHURIZATION OF A SULPHUR-AND-NAPHTHENE CONTAINING CRACKED PETROLEUM NAPHTHA, WHICH PROCESS IS SELFSUPPORTING WITH RESPECT TO THE HYDROGEN NEEDED AND IS PRODUCTIVE OF A DESULPHURIZED CRACKED NAPHTHA HAVING, EXCEPT FOR LOWERED SULPHUR CONTENT, PROPERTIES AND BOILING RANGE SUBSTANTIALLY THE SAME AS THE FEEDSTOCK, COMPRISING THE STEPS OF: PASSING THE SULPHUR-AND-NAPHTHENE CONTAINING CRACKED NAPHTHA AT A SPACE VELOCITY OF FROM ABOUT 0.5 TO ABOUT 1.0 V./V./HR. TO A REACTION ZONE AND CONTACTING THE CRACKED NAPHTHA THEREIN WITH A DEHYDROGENATION-HYDROGENATION CATALYST AND WITH HYDROGEN DERIVED SOLELY FROM THE CRACKED NAPHTHA, SAID CATALYST BEING RESISTANT TO SULPHUR POISONING AND COMBINING ACTIVITY FOR THE DEHYDROGENATION OF NAPHTHENES IN SAID CRACKED NAPHTHA WITH ACTIVITY FOR THE HYDROGENATION OF ORGANICALLY COMBINED SULPHUR IN SAID CRACKED NAPHTHA TO HYDROGEN SULPHIDE; ESTABLISHING A TEMPERATURE IN SAID ZONE IN THE RANGE OF FROM BETWEEN ABOUT 780* F. TO ABOUT 800* F. AT WHICH HYDROGEN IS PRODUCED CONTINUOUSLY FROM SAID CRACKED NAPHTHA; ESTABLISHING A PRESSURE IN SAID ZONE IN THE RANGE OF FROM ABOUT 25 TO ABOUT 75 LBS./SQ. IN. GAUGE, THE TEMPERATURE AND PRESSURE ESTABLISHED WITHIN SAID RANGES BEING CORRELATED TO PROVIDE, FROM THE DEHYDROGENATION OF NAPHTHENES CONTAINED IN SAID CRACKED NAPHTHA, HYDROGEN IN AN AMOUNT AT LEAST EQUAL TO BUT NOT SUBSTANTIALLY IN EXCESS OF THAT REQUIRED TO EFFECT CONVERSION OF SAID ORGANIC SULPHUR COMPOUNDS TO HYDROGEN SULPHIDE AND TO SUPPLY THE HYDROGEN REQUIREMENTS IN SAID REACTION ZONE; SEPARATING A HYDROGEN-RICH GAS MIXTURE FROM THE TREATED PRODUCT, RECYCLING SAID HYDROGEN-RICH GAS MIXTURE TO SAID REACTION ZONE AT A RATE IN THE RANGE OF FROM ABOUT 1000 TO ABOUT 4000 CU. FT./BBL. AT WHICH THE NECESSARY PARTIAL PRESSURE OF HYDROGEN WILL BE MAINTAINED IN SAID ZONE, SAID MIXTURE CONSTITUTING THE WHOLE OF THE HYDROGEN SUPPLIED TO SAID ZONE; AND, RECOVERING THE DESIRED CRACKED NAPHTHA PRODUCT FROM THE RESIDUE OF SAID SEPARATING OPERATION. 